hey scissors - i have mainly mp3's on my ipod. a lot of stuff has been encoded in itunes, but some i have not encoded myself, so i am not sure exactly what encoder was used.
as far as the compression goes, i have primarily 320 kbps files, fewer 192 kbps files and hardly any 128 kbps files.
i went through all of the testing within 6-8 hours of listening, so i will allow you to make your own judgments regarding the importance of this. i will assure you though, that i feel very confident in all of my comments and analysis about the ER-4's.
i think it is very important to say this: if you are biased or unfair in some way during the course of attempting to "compare" or "test" different headphones, no matter how long you spend with them, you will not create a fair and balanced review. although i could have potentially spent weeks with the etymotics, i truly to not believe any of my views on them would have changed. i spent enough time, until i felt i had a solid view on them.
in my review i really did try to be fair. i made good comments about the etymotics where i thought they were deserved; they do have higher textural resolve than the shures, and this shows through mainly on orchestral music.
this is the best thing that the etys have going for them, and if you want high-end detail above all else, the etymotics DO WIN. however, this extra texture, like has been said before, can potentially come at the price of listening fatigue rather quickly. (for me this turned out to be true.) the etymotics also seem to have a lack of tonality, impact and resonance when compared to the shures, perhaps these can be justifications for the shures higher price tag. this is something clearly evident after just a few moments of listening.
everything that i described contributes to the overall sonic signature of each phone, which for the most part, does not change. and for this reason i do not even feel whether i tested with wav's or mp3's is that important to the reader. yes there are quality differences i can notice between 128 kbps files and 320 kbps files, but it equally effects both headphones, i am aware of it, and consciously made sure not to end up taking points away becase the treble sounded poor on the shures or the etymotics because of the 128 kbps file being played. that is a mistake i would never make.
as far as the selection of music goes, i considered going through each song and saying how much i liked it, but this would have gotten pointless by about the third song. think about it this way: my views on the sound representation for each phone never changed, and it would not change from song to song. for the same reason i think the etys sound good in orchestral music due to their higher-frequency textural resolve, i still think they sound good in that respect for that same reason on any other music that has a violin, whether it be greig, or yellowcard. what i thought was more important, was to focus on specific characteristics and detail, what was good or bad, about the ER-4 and the E5. i would also expect people to infer, based on what i wrote, that if they are looking for solid bass, they should expect the E5's to be much better in that regard whether it be for the timpani in an orchestral piece or the bassline in a techno song.
i guess i really do not believe that the quality of the song or the type of music listened to is worth mentioning when it comes to a review like this. i think what is most important is mentioning the specific sound qualities of each, in an effort so that readers can hopefully recognize and understand what is being said, and say, "yeah, that's the kind of sound i am looking for in a headphone." i think the type of music, and the quality it is encoded at, is ultimately irrelevant, as long as you make sure not to hold it against the headphone, which i certainly did not.
basically, what i said in my review is really what i would tell you overall you can expect to hear, if you listen to any music on an ipod with the ER-4 or E5.
i hope this answers your questions.